The present invention relates to an electrical transmission arrangement for use preferably within the microwave band in association with strip-line conductors. The invention is primarily intended for applications where there is need to transfer electrical signals in strip-line conductors in crossing directions.
When transferring electrical signals in the microwave band, primarily in transmission arrangements such as circuit cards and in antenna applications, strip-line conductors are normally used. A strip-line conductor comprises a normally flat conductor and an upper and lower associated ground plane, where the ground planes are separated from the conductor by a dielectric material. The ground planes are also normally flat and arranged mainly in parallel with the conductor at an essentially constant distance from the latter.
A strip-line conductor normally has its main extension in the transmission arrangement in the direction in which it is desired to transfer signals. If it is found to be desirable to transfer signals in strip-line conductors in two different directions, problems can, therefore, occur if these directions cross one another since the strip-line conductors will then run into each other if one of the components included in one strip-line conductor is located in a same plane as a component from the second strip-line conductor.
One way of allowing two strip-line conductors to cross the directions of extension of each other without the strip-line conductors running into each other is to arrange the two strip-line conductors on separate planes in the transmission arrangement. However, this would lead to a solution which requires much space in the transmission arrangement. Furthermore, such a solution would provide poor insulation between the two strip-line conductors since the requirement for saving space in the circuit card would lead to the strip-line conductors being placed as close to one another as possible, with interference between the conductors on both sides as a consequence.
The problem solved by the present invention is to allow two strip-line conductors to cross one another in their main directions of extension with high insulation and in a relatively little space in an electrical transmission arrangement such as a circuit card or an antenna arrangement.
This problem is solved with the aid of an electrical transmission arrangement comprising a first strip-line conductor which has its main extension in a first direction in a first plane in the transmission arrangement and comprises a conductor, an upper ground plane which is situated at an upper distance from the conductor and a lower ground plane which is situated at a lower distance from the conductor. The transmission arrangement also comprises a second strip-line conductor which has its main extension in a second direction in a second plane in the transmission arrangement and comprises a conductor, an upper ground plane which is situated at an upper distance from the conductor and a lower ground plane which is situated at a lower distance from the conductor. The ground planes in both strip-line conductors are separated from their respective conductors and from one another by a dielectric material.
At at least one point in the transmission arrangement, the lower ground plane of the first strip-line conductor coincides with the upper ground plane of the second strip-line conductor.
At the point where the lower ground plane of the first strip-line conductor coincides with the upper ground plane of the second strip-line conductor, the main direction of extension of the first strip-line conductor crosses the main direction of extension of the second strip-line conductor. The second strip-line conductor extends in a third plane in the transmission arrangement at this crossing point whereby the second strip-line conductor exhibits electrical connections between adjacent planes, which connections connect the conductors of the second strip-line conductor, the upper ground plane and the lower ground plane to corresponding components in adjacent planes.
To further reduce the losses at the crossing point, it may be advantageous to allow the second strip-line conductor in a transmission arrangement of the type described above to have a part of its extension in yet another plane, a fourth plane, where the extension in the fourth plane is situated between the extensions of the second strip-line conductor in the second and the third plane. In this embodiment, the said electrical connections between adjacent planes, of the second strip-line conductor, constitute connections between the second and the fourth plane and connections between the third and the fourth plane, which connections connect the conductors of the second strip-line conductor, upper ground plane and lower ground plane in the second and, respectively third plane to the corresponding components of the second strip-line conductors in the fourth plane.
An alternative way of allowing two strip-line conductors to cross each other""s main direction of extension in a space-saving manner and with high insulation in an electrical transmission arrangement is to allow the arrangement, in the same way as has been described above, to comprise a first strip-line conductor which has its main extension in a first direction in a first plane in the transmission arrangement, to comprise a conductor, an upper ground plane which is situated at an upper distance from the conductor and a lower ground plane which is situated at a lower distance from the conductor. Such an arrangement also comprises a second strip-line conductor which has its main extension in a second direction in a second plane in the transmission arrangement and comprises a conductor, an upper ground plane which is situated at an upper distance from the conductor and a lower ground plane which is situated at a lower distance from the conductor, where the ground planes are separated from their respective conductors and from one another by a dielectric material.
In this embodiment of the invention, the main direction of extension of the first strip-line conductor crosses the main direction of extension of the second strip-line conductor at at least one point, but in contrast to the embodiments which have been described above, the first strip-line conductor extends in a third plane in the transmission arrangement at the crossing point, and the second strip-line conductor extends in a fourth plane in the transmission arrangement. The first strip-line conductor exhibits electrical connections between the first and the third plane, and the second strip-line conductor exhibits electrical connections between the second and the fourth plane, where the connections connect the conductor of the first strip-line conductor, upper ground planes and lower ground planes in the first plane to the corresponding components in the third plane, and the conductor of the second strip-line conductor, upper ground plane and lower ground plane in the second plane to the corresponding components in the fourth plane.
In contrast to the two embodiments of the invention described in the introduction, the third and the fourth plane in this embodiment are situated in the transmission arrangement in such a manner that the perpendicular distance between the lower ground plane of the first strip-line conductor and the upper ground plane of the second strip-line conductor increases at the crossing point, instead of these two ground plane coinciding at the crossing point.
To further reduce the power losses in a transmission arrangement according to the invention, ground planes and conductors should be constructed in such a manner that all points on the conductor essentially exhibit the same capacitance with respect to the ground planes. This is suitably brought about by the connections between different planes of the conductor of a strip-line conductor passing an edge in a ground plane, which edge is constructed for impedance matching. In a preferred embodiment of the invention, this construction gives an elliptical shape to at least a part of the edge.